The present invention relates to a drive source for a fire fighting apparatus comprising spray heads, the drive source comprising a hydraulic accumulator, which comprises a container with extinguishing liquid and a pressure gas source for driving the extinguishing liquid out of the container via a channel to the spray heads.
Fire fighting apparatuses utilizing sprinklers and spray heads spraying liquid mist have become more and more usual during the last years. The extinguishing medium is water or water containing additives. Such extinguishing medium is not only environmentally friendly, but also capable of extinguishing fires of different types effectively. On account of that the water is sprayed as a mist, the water damages will be minimal. Gas can be mixed with the water mist in order to obtain very finely divided mist, i.e. mist where the size of the water droplets is extremely small.
In order that the fire fighting apparatuses spraying liquid mist may operate effectively, they are normally fed with high pressure. Such a pressure can be obtained from high pressure pumps and pressure gas containers. The pressure gas containers are often preferred, because they can function independently without the need of external energy. On account of this, combinations of liquid containers and pressure gas containers constitute common drive sources in this connection. These drive sources are called hydraulic accumulators.
A problem with liquid containers containing water is the risk of ice formation when the liquid containers are emptied under high pressure. If a rising tube of the water container delivering liquid out of the water container freezes, it can be clogged, whereby the delivery of extinguishing medium is hindered or entirely interrupted.
When hydraulic accumulators are used, the size of the water droplets becomes bigger and bigger toward the end of the emptying process. This is not desirable normally. For that reason, it is known (WO 94/08659) to mix gas with the water delivered out of the water container in order to keep the droplet size small enough.